1. Field of the Invention
The present invention relates to an improvement in the powder filling machine of capacity type. Particularly, it is concerned with a machine capable of supplying each measured amount for a single shot of any powdery or particulate material of varying bulk density to a container transferred in succession to be placed underneath the measuring mechanism.
As is known, this type of powder filling machines have been and are now widely used by food or pharmaceutical manufacturers, because they are usually simpler in mechanism and less frequent trouble than those of weighing type. Among these, a vial filling machine is in practical use in pharmaceutical industry.
2. Description of the Prior Art
The known various vial filling machines of capacity type can be roughly classified into the following two groups, according to the difference in mode and means for measuring the powder to be filled and for supplying the measured powder to the container; one of which is based on a system comprising, suctioning the powder into a cylinder of a predetermined capacity radially disposed along a circumference of a vertically supported rotating disk and then pouring the measured amount of powder to a vial with gravity and pressure, and the other is based on a system comprising, rotating a compact screw feeder confined in a filling chute filled with powder for a predetermined turn or angle.
Of these known vial filling machines, the former one wherein the amount of powder to be filled for a single shot is determined by the fixed capacity of the cylinder, needs an interruption of the operation when the determined amount has to be changed.
In addition to this, such machines cannot prevent a large fluctuation (irregular level) in the amount for a single shot due to the difference in the bulk density of the powder to be filled, and this fluctuation cannot likewise be corrected without interrupting the filling operation.
Furthermore, since the measuring operation in accordance with this system is performed by direct levelling with a levelling blade adjacent to the rotating disk and the levelling may cause a contamination of the powder to be filled with any foreign particles, any countermeasure for such hazard has long been desired.
Conversely, if the filling operation is performed in accordance with the latter system wherein the change in the filling amount can be attained by varying the time period for actuating the rotating screw feeder, the correction can be made during the operation without interrupting it. The rotation of the screw feeder, however, may occasionally cause an adhesion of the powder, which may have various undesirable properties for instance, stickiness, to the feeder and other components inside the chute to result an unexpected and marked decrease in the filling amount. This is another undesirable feature causing serious fluctuations in the filling amount, inherent to this system.
Disadvantages in the actual filling operation which may be attributable to such defects of the known filling machines may easily be understood by any person skilled in the art.